I have three old joist hangers (thick steel--house built in 1936) that are in place to support joists attaching to doubled headers where the ash dump runs below the first floor fireplace. Two wider joist hangers attach to the adjacent joists to support the headers as well. Here's the thing: none of the relevant joists or headers actually rests in its hanger--they all have 1/4-5/8" of space between the bottom of the joist and the bottom of the "U" of the hanger. Has anyone encountered this? Could it be indicative of something else going on in the house? The joists in question are either level or quite close to it. The first floor is a tad bouncy, but I had been attributing this to one cracked joist and to twin, 4-5" deep, center-span notches in each of two joists that some previous owner made to accommodate recessed lights! Arggh! I'll be sistering these shortly... In any event, since the new drop ceiling will go flush on the joists, I would love to remove or cut the bottoms off these hangers if, in fact, they are doing nothing. In truth, I can't really even imagine doing this, because it just sounds so stupid, but if the joists aren't sitting in them, how could they be serving any purpose? Probably I will end up boxing around them, but still, I am curious about this situation. Thanks for your thoughts.

Its not uncommon to find those heavy joist hangers not holding up the floor joists. What has happened is the framing has shrunk and no longer rests on the bottom of the hangers. If you were able to take this apart you would find additional nails hidden holding up the joists.

Do not cut or modify these hangers in any way. You can if you like cut wood wedges and hammer them into the space to help hold the joists. It may not do anything but make you feel more comfortable knowing that they are now holding up something.